Indoor air pollution is ranked as a leading cause of illness according to the Environmental Protection Agency and respiratory problems are now the top reason for admissions to hospitals in the U.S., over all other ailments. Given that people in the United States spend as much as 90% of their time indoors, a way must be found to effectively remove toxins from indoor air easily and effectively, while doing so in a way that limits heating and cooling costs.
The customary way to clean poor indoor air is through ventilation, by taking poor indoor air and expelling it outside the building, than replacing it with purer outdoor air. Unfortunately mechanical ventilation is effective only when outdoor air is relatively clean and when the cost of bringing the temperature of that air up to or down to a normal human comfort level is low. Today, however, outdoor air can be quite polluted, especially in large metropolitan centers, while the costs of heating or cooling outdoor air when it is brought inside are quite high. Thus a method must be found which limits mechanical ventilation and transforms the toxins within indoor air into harmless or even beneficial substances.
Most indoor air pollution control systems do not transform toxins within the air into harmless substances and as such they do not cut down dramatically on the need to mechanically ventilate a structure. Nor do most such systems clean the air of both particulate matter and airborne volatile organic compounds (VOCs) which off-gas into the air from carpets, furniture, wallboard, computers, copying equipment, cleaning agents and human beings themselves. With buildings becoming more and more air-tight to save on rising energy costs, the danger to human health has only increased. Therefore a cost-effective system must be found to deal with this problem.
Presently, there are many systems available for treating poor indoor air which contains both particulates and organic toxins. Hot and cold electrostatic precipitation, bag, filter bag and hepa filters and mechanical precipitators have been used, but all are substantially limited to the removal of particulate matter. Scrubbers—particularly wet scrubbers—provide the most effective means to control both particulate and gaseous pollutants. More often than not, however, these are used in industrial processes, but rarely have been used in residential or commercial structures. One reason for this is because of the increased humidity which wet scrubbers generate. This increased humidity can be trapped within a structure and give rise to mold and mildew problems.
Wet scrubbers typically employ or have within them a scrubbing zone where air is restricted and where gasses pass through layers of a filter with many impingement surfaces so that the gas is cleaned by agglomeration and absorption. In addition, wet scrubbers, by coating all surfaces within the filter bed with moisture, cause certain chemicals or VOCs to adhere to the moisture droplets, whereby the structure of these toxins is changed when they combine with the moisture itself. For instance, formaldehyde reacts with water to form methylene glycol, in the reaction CH2O+H2O→CH2(OH)2. Or, in the presence of air and moisture at room temperature, formaldehyde readily polymerizes to form paraformadehyde—a white crystalline solid form of formaldehyde gas (typically 90-97% pure).
Standard chemical adsorption filters utilize certain substances which adsorb other substances or chemicals. In the case of air purification, activated charcoal is often utilized. But, while activated charcoal adsorbs certain types of volatile organic compounds, it is ineffective in adsorption of other VOCs such as Formaldehyde.
It is known that there are a wide range of VOCs—as many as 900 or more in some indoor air—and that no one form of extraction of VOCs has found to be effective for all. Some VOCs are adsorbed by activated carbon. Some dissolve in moisture. Therefore a mechanism or a combination of mechanisms needs to be employed which traps all the VOCs and eventually converts them into a harmless material to humans. Otherwise the need for ventilation still exists.
U.S. Pat. No. 5,756,047, in column 1 starting at line 30, surveys some of the prior art, stating that: “scrubbing may occur in a bed packed with a solid having a large surface area, thereby increasing the surface area at which the liquid and the gas may contact each other, as shown in Lonnes et al., U.S. Pat. No. 3,969,479; in a reaction chamber in which a mist of the liquid contacts the gas, as shown in deVries, U.S. Pat. No. 4,844,874; or in filters, as shown in Fritz, U.S. Pat. No. 4,784,835.”
In contrast to the artificial systems of these above patents, plants naturally remove pollutants from the air. They do this by absorbing such pollutants through their leaves and then transporting the toxins down to the root system where the microbes, around the root system, consume as food and digest the toxins, changing them into harmless substances.
But these toxins will be digested by the microbes even if they pass directly through the filter bed, rather than being delivered thereto by the plants. Thus, it is known that by using a mechanical device which pulls air directly through the filter bed, indoor air can be pulled directly down to where the plants' root systems are and to where microbes congregate. As a result one plant can do the air-cleaning work of hundreds of plants, since the plant itself no longer serves as the main transport mechanism for these toxins and the number of microbes in the filter bed will multiply by virtue of their enhanced food supply. Further, plants grown within the filter bed have a symbiotic relationship with the microbes which digest the pollutants, fostering a conducive atmosphere which allows the microbes to flourish.
The prior art does appear to disclose the use of wet scrubbers which are, in essence, a filter bed in which plants are grown and in which microbes live. See, for example, U.S. Pat. Nos. 4,975,251; 5,044,120; 5,130,091; 5,217,696; 5,269,094; 5,277,877; 5,397,382; 5,433,923; and 6,230,437.
Thus, it appears to be well-known that moisture can scrub the air of certain well known VOCs such as formaldehyde and that if plants and microbes are grown in a filter bed, that such a configuration can also be used to purify indoor air. Yet this very same moisture can bring on mold and mildew if it finds its way into the dark and tightly-confining ducting of a building's HVAC system, or if excess amounts of moisture are trapped within a tightly-sealed building.
Thus, the moisture required to allow microbe transport within the filter bed and also to prevent mold and mildew—its delivery and distribution, and its absorption by plant roots and dissipation by evaporation and air flow—needs to be carefully and deliberately controlled.
Nonetheless, in all of the prior art in this field, the proper moisturizing of the plant/filter bed is barely considered, or is mentioned merely at the most-cursory level. The prior art appears to neither disclose nor suggest employing micro irrigation system in a way that ensures uniform moisture distribution. Nor is the prior art overly concerned with distributing water below the plant canopy or dealing with the potential for mold and mildew. Thus, for example, in an exemplary prior art U.S. Pat. No. 4,961,763 to Thompson, it is stated in column 8, starting at line 24:
“If desired, moisture sensors may be included with the air purifier for assuring that the soil bed remains moist. Either electronic or chemical moisture sensors may be used. For example, soil conductivity may be measured and used to indicate water content. If desired, instead of just measuring soil moisture, such electronic sensing may be employed for making controlled additions of water to the bed of soil in the air purifier. Drip irrigation may also be used.”
In fact, the “drip irrigation” method disclosed in Thompson does not saturate the filter bed. It only saturates spots in the filter bed, in a non-uniform manner. Nor does the use of moisture sensors alleviate this problem, because each sensor is localized and so cannot be used to ensure a uniform distribution over substantially the entire active regions of the filter bed. This is not conducive to the maintenance of microbes and microbial transport within the bed, because what is also critically important is the uniformity of the irrigation delivery. To date, this uniformity of irrigation simply does not appear to have been addressed in the prior art, and appears to be a shortcoming in the state of the art.
In particular, it can be demonstrated that drip irrigation is a very inefficient way to saturate a filter bed. At best it only provides a wet spot of maybe an inch to an inch and a half around each dripper. Such “drippers” are designed specifically to get moisture only to where the roots of the plant are located, not to saturate the entire filter bed so as to allow microbes to live and work in the entire filter bed. Thus, while suitable to maintain the plant life, such drip systems are less-than-optimal for an air cleansing system in which microbial maintenance is equally important not only to plant maintenance, but to the removal of toxins in air which is transported through the filter bed for the express purpose of removing toxins by feeding them to microbes. The purpose of a dripper is to conserve water by only delivering water to the plant roots, not to deliver water throughout the bed and sustain microbial transport for toxin removal and filter bed bioregeneration.
It would be much preferred to evenly deliver irrigation to the surface of the entire filter bed for at least 2, and up to 12 to 24 inches in all directions from each individual irrigation source outlet, in combination with a suitable network of source outlets, thus providing saturation of the entire filter bed so as to allow microbes to live and work in the entire filter bed. Further, with a more-uniform irrigation delivery, even saturation of the filter bed gives added capability to the wet scrubber effect, independently of this positive microbial impact, and serves to bioregenerate the filter bed in a completely natural manner.
Beyond the limitations of drip irrigation, Thompson shows irrigation source outlets which are not placed close to the filter bed surface (within twelve inches or less of the bed surface, and even below the bed surface). Nor are they placed below the majority of leaves of the plants growing in the filter bed. Thus, leaves will deflect the irrigation delivery, further compounding the problem of non-uniform irrigation delivery. It is much preferred to place the moisturizing emitters (irrigation source outlets) below the surface of the leaf canopy of the plants grown within the filter bed.
In sum, it is desirable to have a device, system and method by which moisture can adequately saturate the filter bed in an indoor air purification system which acts as a wet scrubber and provides proper sustenance for the needs of plants and microbes which live within the filter bed, and simultaneously, which does not give rise to mold and mildew within the building.
It is further desirable to ensure a highly uniform delivery of irrigation to the plant/filter bed, not only to maintain the plant matter, but also to facilitate microbial transport to bioregenerate the filter bed and enhance the area over which wet scrubbing can take place. This includes improving the method of delivering water to the plant/filter bed, and ensuring that the plant matter itself does not interfere with this delivery.